Dividing and amplifier circuit for electronic organs



F. M. SCHMIDT July 10, 1951 DIVIDING AND AMPLIFIER CIRCUIT F'OR ELECTRONIC ORGANS Filed Jan. 8, 1948 2 Sheets-Sheet l foal L W w 0 C Z6 1k wof F. M. SCHMIDT July 10, 1951 DIVIDING AND AMPLIFIER CIRCUIT FOR ELECTRONIC ORG-ANS 2 Sheets-'sheet 2 Filed Jan. 8, 1948 'y Maw/1% @a Patented July 10, 1951 DIVIDING AND AMPLIFIER CIRCUIT FOR ELECTRONIC ORGAN S Francis M. Schmidt, North Tonawanda, N. Y., assignor to The Rudolph Wurlitzer Company,V North Tonawanda, N. Y., a corporation of Ohio Application January 8, 1948, Serial No. 1,115

15 Claims. (Cl. 841.21)v

vThis invention relates to dividing and amplier Vcircuits for electrical musical instruments, and concerns particularly the speaker control circuits for electronic organs.

VIn the operation of electrical musical instruments,` and specifically electronic organs of the type to which the present invention particularly relates, there is provided a plurality of banks of tone generators which are selectively operable to generate tones in the form of electrical waves, the waves being combined, amplified, and transmitted to speaking apparatus wherein they are transformed and emitted as sound. In such instruments it is frequently desirable to provide a plurality of sound emitting devices, such as loud speakers, disposed at various preselected locations in respect to the room or other chamber within which the instrument is to be played. Furthermore, it is desirable that the amplification of the generated tones be effected in a plurality of stages, the initial amplifier stages effecting the tone shaping, and the nal stages being more directly associated with the speakers and facilitating the proper operation thereof. The present invention concerns more directly the division of the generated tones, after partial am* pliiication and shaping, and the further amplication thereof and emission as sound within the speaker devices.

.It is an object of the present invention to pro- 1:

vide an improved dividing and amplifier circuit for electrical musical instruments, and particularly for electronic organs of the type defined.

More specifically stated, it is one of the objects of the present invention to provide an improved dividing network for electronic organs, wherein a plurality of speaker devices either proximately or remotely disposed may be interconnected with a single tone generating source, with a minimum of interference and maximum facility, and by means of improved switching structures.

YA further object of the invention is to provide in a tone generating and reproducing system of the type dened, improved tone or electrical impulse .dividing and amplifying means, effective to preserve the wave shape of the oscillations or pulsations delivered thereto, and operable to insure proper speaker operation over a wide range of frequencies without undesired speaker intermodulation.

Various other objects, advantages and features of the invention will be apparent from the following specification when taken in connection `with the accompanying drawings, wherein a preferred embodiment is set forth for purposes of illustra-l tion.

In the drawings, wherein like reference 11u-4 merals refer to like parts throughout:

Fig. l is a diagrammatic view of an electrical.

musical instrument, and specifically an electronic organ, incorporating a tone producing, dividing, and amplifier circuit constructed in accordance with and embodying the principles of the invention;

Fig. 2 is an electrical schematic diagram. of.:Y

the system;

Fig. 3 is an electrical diagram and schematic fview, more particularly showing one of the tonev over-all volume or level of the instrument may'A be controlled, and a series of stop tablets 2|) by means of which the various tone generators are caused to be activated and the Volume thereof controlled, in banks, in the particular instrument shown.

Further disposed within the console casing IU is a plurality of banks of tone generators 22 which may, for example, be of the type and kind shown in the patent to Hoschke No. 2,015,014. More specifically, and as shown in Fig. 4, these tone generators comprise a series of vibratory reeds 24 individually disposed within cells 28, each reed having associated therewith an adjustable pickup screw 28 forming with its associated reed a capacitor variable in accordance with the reed vibrations. Air is admitted to the cells 26, so as to cause the selective vibration of the reeds, by means of a series of pallet valves 3Q, the selective operation of which is controlled conjointly by the keys of the manuals, and those of the. pedal clavier, as determined by the operation of"l the stops 29. This control is effected by coupler boards as shown at 32 and 3d, the coupler boards4 containing switches selectively actuated by the keys of the manuals and pedalv clavier, .in accordance with the selected stops. which have been depressed, so as to cause the operation of the desired pallet valves to thereby admit actuating air The .air supply for l tovibrate the desired reeds. the reeds is provided from a blower 3,6.

The electrical output from the tone generators There is also provideda or reeds is transmitted to a first stage amplier 38 within the console, the volume control mechanism 48 operated by the swell pedal I8 being associated with said amplifier 38, so as to effect the volume control of the instrument.

The stops 28 not only select the pallet valves for operation, but also control the intensity of various of the reed banks, the stop controlled intensity switches being illustrated at 42, 44 and 46 in Fig. 2.

Remotely disposed in respect to the organ console, and connected thereto by a cable 48, Fig. 1, is a series of tone outlets, which in the specific embodiment illustrated in Fig. 1 comprises a pair of main tone cabinets 5|) and 52, and an echo tone cabinet 54. The details of the mechanisms disposed in the tone cabinets, and the connections therefor, form a part of the present invention and will hereinafter be more specifically described.

Referring to the schematic wiring diagram, Fig. 2, it will be seen that there is provided a rectifier unit 56, which may preferably be of the full wave electronic tube type, powered from a suitable source of A. C. supply as indicated at 58. The'negative D. C. line 60 from the rectifier is connected to ground through a resistor 62, whereas the positive D. C. wire 64 leads to a bank of seleste reeds 66 through a resistor 68 and `wire 69, and to a bank of diapason reeds 18 through a resistor 12, as shown.

4The D. C. supply line 64 is further connected by means of a variable resistor 14 with a bank of viole reeds 16, and by means of a variable resistor '|8 with a bank of pedal `reeds 80, and by means of a variable resistor 82 to a bank of fiute reeds 84.

,A predetermined greater voltage may be applied to the viole reeds through a resistor 86 by the closing of stop switch 46, and to the pedal reeds through a resistor 88 by the closing of stop switch 44, and to the flute reeds through a resistor 90 by the closing of the stop actuated switch 42.

, As best shown in Fig. 4, wherein a group of the celeste reeds is specifically shown, the reeds are connected in parallel to their polarizing voltage supply source, and to ground through a suitable resistor as indicated at 92.

By means of the described connections polarizing voltages of predetermined selective intensity may be Variably applied to the reed banks. These connections are more specifically set forth in my copending applications, Serial No. 1,112 and Serial No. 1,113, filed of even date herewith, to which reference may be made, if desired.

lAs also best shown in Fig. 4, it will be seen that the tone screws or pickups 28 are connected in parallel to an output wire as indicated at 94 in the case of the celeste reeds, this wire leading to the preamplifier 38. Similarly the tone screws of the remaining reed banks are connected to the preamplifier by suitable connections as indicated at 96, 98 and |00. The signal circuit to the preamplifier further includes a capacitor as indicated at |02, in by-pass relation to each of the resistors 92.

As more particularly pointed out in said Hoschke patent, the reed vibrations produce electrical oscillations or pulsations transmitted to the amplifier, the intensity of which is controlled by the magnitude of the polarizing Voltages. The tone quality of each reed bank is different, as indicated by the name designations applied thereto, such quality differences or differences in generated wave shape being due, in part, to control of the physical relationships in the tone screw-reed capacitors.

As more particularly pointed out in my U. S. Patent No. 2,555,295, granted May 29, 1951, wherein the details of the preamplifier 38 are particularly set forth, the wave shapes generated by the reed vibrations are further controlled. preserved, or modified within the preamplifier structure by various wave shaping components, whereby the output tones or waves from the preamplifier will have the desired shape or quality. and proper harmonics, throughout the full frequency and intensity range of the instrument. The present invention concerns the means and methods by which the output tones, or more accurately stated the output electrical oscillations from the preamplifier 38, are further amplified and their wave shape preserved, and transmitted to the several desired tone outlets.

As more particularly pointed out in said copending application, Serial No. 1,114, the preamplifier 33 comprises a plurality of amplifier stages, the final Class A power tube of which feeds a transformer herein illustrated in Fig. 2 at |64, having a primary |06 and a secondary |88.

Referring further to Fig. 2, and in accordance with the present invention, it will be seen that one end of the transformer secondary is connected directly to ground by means of a line H3, whereas the other end of the secondary is connected to ground through a line and a pair cf series-connected resistors ||2 and ||4 forming a voltage divider. A pair of resistors H6 and El@ forming a second voltage divider is connected to ground in parallel with the resistors M2 and H4, as shown. A variable tap connection |28 leads from the resistor ||4 by means of a line |22 to the echo tone cabinet 54, whereas a variable tap |24 connects with resistor ||8 and leads by means of lines |25 and |28, respectively, to the main tone cabinets 5D and 52. A suitable source of A. C. power supply, as indicated at |38, is also interconnected with the several tone cabinets, as shown, the wire connections to the tone cabinets being effected through socket plugs |32, |34 and |36. By way of illustration, the A. C. supply wires to the tone cabinet 5U are indicated by the reference numerals |38 and |40.

A line |42 interconnects the midpoint between resistors ||2 and 4 with a normally closed switch |44 adapted to be opened by the depression of a manually operable stop tablet |46. Switch |44 is seres-connected to ground through the normally closed contacts |43@ of a second' switch structure |48, arranged for operation by a second manually operable stop member, as shown at |58. The normally opened contacts |431) of this latter switch are interconnected by means of a line |52 with the midpoint between resistors ||6 and H8. Depression of the stop |58 opens switch contacts |4311 and closes contacts |4819.

W'hen the switches |44 and |48 are in the position illustrated in Fig. 2, line |42 shorts the resistor H4 so that the echo tone cabinet 54 is inoperative; whereas line |52 is in open circuit condition so that resistor ||8 is operative to transmit a predetermined fraction of the signal output from the preamplifier to the tone cabinets 5|] and 52. The fraction thus transmitted to the main tone cabinets 50 and 52 is determined by the proportioned resistance values of the resistors |2||8, as well as by the position of the adjustable tap |24.

Depression of stop. |48 opens switch |44, thus throwing short circuit line |42 into opened circuit condition and thus rendering resistor ||4 operative to transmit a predetermined fraction of a signal through adjustable tap |28 to the echo tone cabinet 54. Under such conditions, all tone cabinets will be operative. Depression of stop |50, While stop |48 remains undepressed, effects an opening of contacts |48a to render the echo tone operative, and a closing of contacts |4819 to render the main tone cabinets 50 and 52 inoperative, so that only the echo tone cabinet will be heard.

The connections thus provided form a simple switching arrangement for selectively energizing the main and echo tone cabinets. The connections furthermore provide ready means by which the signal fraction to be transmitted to the several tone cabinets may be adjusted for volume intensity control, as desired; and, still further, the arrangement of the parallel resistors is such that a minimum disturbance will result in the operation of one tone cabinet when another is rendered selectively operative or inoperative. f additional tone cabinets are added to the system, suitable compensating adj-ustments may be readily made by the taps |20 and |24. The operation of the stops |48 and |58 merely controls the disabling of short circuits and thus a minimum of shock is transmitted to the tone cabinet circuit as the stopV switches are selectively actuated.

Referring further to Fig. 2, it will be seen that each main tone cabinet includes a divider |54 and a pair of amplifiers |58 and |58, supplied thereby, each ampli-fier being provided with a pair of speakers, as indicated at |88. The echoY tone cabinet may be similarly constituted or, as shown in Fig. 2, may comprise an amplifier |82 feeding to a divider |84 which, in turn, supplies a pair of loud speakers, as indicated at |88. The dividers and amplifiers may be similarly consti tuted. The specific construction for the tone cabinet 50 is set forth in Fig. 3.

Referring to Fig. 3, it will be seen that the junction and divider unit |54V comprises a low pass' filter |88 and a high pass filter |10. More specifically, the low pass filter comprises a wire |12 interconnecting with the signal or tone supply wire |28, and leading to an isolating resistor |14. This resistor interconnects with a series choke |16 and a capacitor |18 to ground, forming a iirst'iilter section. The low pass filter further comprises a series resistor |88 and a ground connected capacitor |82, forming a second filter section, andA a terminating or loadresistance to ground, as indicated at |84. Wire |88 interconnects the low pass filter with the lowr frequency amplifier |58 feeding a pair of loud speakers |80, as previously described. The amplifier |50 is preferably of identical structure with the high frequency amplifier |58, presently to be described.

The high pass filter |10 comprises a line |88 interconnecting with the signal supply, which line leads to an isolating resistor |80. The lter further comprises a pair of series-connected capacitors |32, a ground connected choke |94, and a terminating resistance to ground in the form of a voltage divider comprisedA of four resistor sections, as indicated at |96, |98, 280 and 202. An adjustable tap switch 204 is arranged S0 that any one of several fractions of the voltage divider may be tapped off and transmitted? to a line 208 leading to the high frequency amplifier. The adjustment 204 insures a proper proportioning of the low and high frequency intensities to accord With the acoustics of the installation wherein the tone cabinet is to be located.

The amplifier |58 comprises a full-wave tube rectier 208 powered from the A. C. supply wires |38 and |40. The positive or B+ D. C. supply line. from the rectier is indicated at 2|0 and the negative return line at 2|2.

The signal circuit wire 208 from the high pass filter connects through a safety coupling capacitor 2|4 to the grid of a voltage amplifier triode 2|6, there being a grid load resistor 2|8 connected to ground as shown. The cathode bias circuit for the tube 2|8 comprises a resistor 220 and a resistor 222 in series, forming a voltage divider, the resistor 220 being by-passed by a capacitor as indicated at 224.

The plate circuit for the tube 2|8 comprises a load resistor 228 interconnected with the B+ voltage supply line 2 I0 from the rectifier through a pair of voltage dropping and isolating resistors 228 and 230. The B+ supply line further includes a series of filter capacitors to ground as indicated at 232, 234 and 236.

The load circuit of amplifier tube 2|8 is connected by means of a coupling capacitor 238 with the grid of a no-gain, phase inverter triode 240 which for convenience may be disposed in a common envelope with the amplifier 2|8, forming a dual triode structure.

The grid load resistor circuit for the phase inverter tube comprises a pair of resistors in series as indicated at 242 and 244, the latter resistor also being in series connection with a rev-- sistor 248 in the cathode circuit of the phase inverter tube, the resistor 248 being by-passed by a capacitor as indicated at 248.

The plate circuit for the phase inverter tube comprises a load resistor 250 connected to the B+ source of supply, said load circuit being connected by means of a coupling capacitor 252 with the control grid of a pentode tube 254, said tube together with a similar pentode tube 258 forming a Class A push-pull amplifier stage.

r`he cathode bias circuit for the push-pull tubes comprises a resistor 258 by-passed by a, capacitor as indicated at 288. The grid load resistors for the push-pull stage are indicated respectively at 282 and 284, the latter being coupled to the cathode circuit of the phase inverter tube through a coupling capacitor 288.

The resistors 258 and 244 are preferably of equal value, and similarly the resistors 282 and 284 are of similar value. The plate resistor 250 constitutes a load for resistor 262, whereas the cathode resistor 244 constitutes an opposed phase load resistor for the resistor 284 in a cathode follower circuit. lThe plate and cathode resistors of the phase inverter tube thus drive the pushpull stage, as will be understood. Resistor 230 constitutes a grid dropping resistor for the screen grids of the push-pull tubes through wire connection 28B, as shown.

The plates of the push-pull tubes are connected to the opposite ends of the primary coil 218 of the speaker load transformer, the primary. coil being center tap connected to the B+ source of supply; and there being a phase correcting or stabilizing circuit comprising a capacitor 212 and a resistor 214 interconnected between the tube plates as shown.

The secondary coil 218 of the load transformer is series connected to the voice coils 218 and 280 of the speakers, the transformer secondary also being center tap connected by means of a line 282 and a resistor 284 to the cathode circuit of amplifier tube 2 it, forming an inverse feed back circuit.

The field coil 285 of one of the speakers is interconnected with the B+ D. C. supply source by means of a wire 238, resistor 230 forming a dropping resistor for the voltage supplied. The field coil 295B of the other speaker is interconnected with the B-lsource of supply through a line 292 and a similar voltage dropping resistor 294. A switch may be opened to disable the second speaker, and when opened causes a normally shorted resistor 298 to be inserted into the return line Edil of the first speaker field coil whereby to maintain the voltage drop therein substantially constant.

The amplifier circuit above described, comprising the ampliiier ii, is characterized by a substantially flat or straight line amplication characteristic over a wide frequency band. The combination of such type amplifier with the high and low pass filter circuits, as described, produces acomposite straight line amplier throughout a wide frequency range in the tone cabinets for cooperation with the preamplier 38, preserving the wave shape imparted to the generated tones in the preamplifier, and producing a minimum of intermodulation between the speakers throughout the volume and frequency range of the instrument. As will be understood, due to the action of the high and low pass filters, the amplifier |55 is provided essentially for high frequency amplification and the amplifier H58 essentially for amplification of low frequencies, in the operation of the structure.

It is obvious that various changes may be made in the specific embodiment set forth for purposes of illustration without departing from the spirit of the invention. The invention is accordingly not to be limited to the specific embodiment shown and described, but only as indicated in the following claims.

-The invention is hereby claimed as follows:

l. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a single composite signal, a plurality of tone outlets, and means for selectively transmitting said composite signal to plurality of outlets comprising a signal circuit, a plurality of resistors disposed substantially in parallel with one another and arranged for connection in said circuit, means for selectively rendering said resistors operative and inoperative, and amplifying means interconnecting said resistors with said tone outlets.

2. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a singe composite signal, a plurality of tone outlets, means for selectively transmitting said composite signal to said plurality of outlets comprising a signal circuit, a plurality of resistors disposed substantially in parallel with one another and arranged for connection in said circuit, means for selectively rendering said resistors operative, an amplifying channel connected to each tone outlet, and adjustable tap means interconnecting said resistors with said tone outlets through the amplifying channels.

3. An electronic musical instrument comprising a plurality of tone generators, means forcombining the output from said generators to form a single composite signal, a plurality of tone outlets, and means for selectively transmitting said composite signal to said plurality of outlets comprising a signal circuit, a plurality of resistors connected substantially in parallel with one another to said circuit, means for selectively short circuiting said resistors, and a plurality of amplifying means each interconnecting one of said resistors with one of said tone outlets.

4. An electronic musical instrument comprisof sets of series-connected resistors arranged for connection substantially in parallel with one another in said circuit, each set of resistors forming a voltage divider, means for rendering the terminal resistor of each set selectively operative or inoperative, and a plurality of amplifying4 means each interconnecting one of said terminal resistors with one of said tone outlets.

5. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a single composite signal, a plurality of tone outlets, and means for selectively transmitting said composite signal to said plurality of outlets comprising a signal circuit, a plurality of sets of series-connected resistors arranged for connection substantially in parallel with one another in said circuit, each set of resistors forming a voltage divider, means for rendering the terminal resistor or each set selectively operative or inoperative, a plurality of amplifying channels and means comprising a series of adjustable taps interconnecting said terminal resistors with Said tone outlets through said plurality of amplifying channels.

6. An electronic musical instrument comprising a plurality of tone generators, means for, combining the output from said generators to form a single composite signal, a plurality lof tone outlets, and means for selectively transmitting said composite signal to said plurality' sistors operative, and means interconnecting said resistors with said tone outlets.

'7. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a single composite signal, a tone outlet including a plurality of speakers, and means for transmitting said composite signal to the speakers comprising an amplifier, a high pass lter, a low pass filter, means for rendering at least one of said speakers inoperative, and means respectively connecting said speakers to said filters, to give a broad frequency range output.

8. An electronic musical instrument comprisying a plurality of tone generators, means for p combining the output from said generators to form a single composite signal, a tone outlet including a plurality of speakers, and means for transmitting said composite signal to the speakers comprising a high pass lter connectedto said combining means, a low pass iilter connected to said combining means, a pair of substantially similar ampliiiers each connected to one of said filters, a circuit interconnecting one lter and amplifier with one of said speakers, and a circuit interconnecting another iilter and amplier with another of said speakers, to give a broad frequency range output.

9. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a single composite signal, a plurality of tone outlets including a plurality of speakers, and means for transmitting said composite signal to the speakers comprising a plurality of ampliiiers, each ampliiier including a pair of tubes in push-pull, and a cathode follower circuit foi feeding said tubes, a high pass filter connected to said combining means, a low pass lter connected to said combining means and means respectively connecting said speakers through said amplifiers to said filters, to give a broad frequency range output.

10. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a single composite signal, a plurality of tone outlets including a plurality of speakers, and means for transmitting said composite signal to the speakers comprising a plurality or" amplifiers, each amplifier including a pair oi tubes in push-pull, a phase inverter tube, and a cathode follower circuit interconnecting the phase inverter tube and push-pull tubes, a high pass filter connected to said combining means, a low pass iilter connected to said combining means, and means respectively connecting said speakers through said ampliers to said lters, to give a broad frequency range output.

11. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a single composite signal, a tone outlet including a plurality of speakers, and means for transmitting said composite signal to the speakers comprising a pair of substantially similar ampliers, each of said ampliiiers including a pair of tubes in push-pull, and a cathode follower circuit for feeding said tubes, a high pass lter, a low pass filter, both of said ilters connected to said combining means, means interconnecting one amplifier and ilter with one oi said speakers, and means interconnecting another amplifier and filter with another of said speakers, to give a broad frequency range output.

l2. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a single composite signal, a tone outlet including a plurality of speakers, and means for transmitting said composite signal to the speakers comprising a pair of substantially similar amplifiers, each amplifier including a pair of tubes in push-pull, a phase inverter tube, and a cathode follower circuit interconnecting said tubes, a high pass filter, a low pass filter, both of said lters connected to said combining means, means interconnecting one ainplier and ilter with one of said speakers, and means interconnecting another amplifier and lilter to another of said speakers, to give a broad frequency range output.

13. An electronic musical instrument comprising a plurality of tone generators, means ior combining the output from said generators to form a single composite signal, and a plurality of tone outlets each including a speaker, a selective filter, and an ainplicr fc-r transmitting said signal from said seiectnefilter to the speaker, said amplifier including an ampliner tube, a phase inverter tube driven thereby, a pair of tubes forming a push-pull amplifier stage, a cathode follower circuit ior driving said pushpull tubes, and an inverse feed back circuit for said first named amplier tube.

14. An electronic musical instrument comprising a plurality of tone generators, means for combining the output from said generators to form a single composite signal, and a plurality or" tone outlets each including a speaker, a selective lter, and an amplifier for transmitting said signal from said filter to the speaker, said amplier including an amplirier tube, a phase inverter tube driven thereby, a pair of tubes forming a push-pull stage, and an inverse feed back circuit for the first named ainplier tube.

15. An electronic musical instrument comprising a plurality or tone generators, means for combining the output from said generators to form a composite signal, a plurality of tone outlets, and means for selectively transmitting said composite signal to said plurality of outlets comprising a signal circuit, a plurality ol resistors disposed substantially in parallel with one another and arranged for connection n said circuit, means for selectively rendering said resistors operative and inoperative, and means interconnecting said resistors with said tone outlets comprising a high pass filter, a low pass filter, and an amplifier associated with each of said iilters.

FRANCIS M. SCHMIDT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,153,756 Hunt Apr. 11, 1939 2,159,505 Hammond May 23, 1939 2,237,105 Miessner Apr. 1, 1941 2,239,775 Bierwirth Apr. 29, 1941 2,310,429 Hanert Feb. 9, 1943 2,349,001 Mcellip et al. Jan. 25, 1944 

